Solve for $z$ : $z + 20 = 12$
Solution: Subtract $20$ from both sides: $ \begin{eqnarray} \\ z + 20 &=& 12 \\ \\ {-20} && {-20} \end{eqnarray} $ $ \begin{eqnarray} \hphantom{20 + z} &\hphantom{=}& \hphantom{12} \\ z &=& 12 {- 20} \\ \end{eqnarray} $ Simplify. $ z = -8$